Recently, cable television systems have begun providing numerous enhanced services to their subscribers. In order to provide those services, the cable system is used to transport data both upstream and downstream along with television signals. Such signals are transmitted in frequency ranges ranging from, currently, 5 Mhz to 860 Mhz. Moreover, the standardized signals and frequency ranges have a significant amount of overlap. TABLE 1 below illustrates the frequency ranges commonly used in a cable system for television programming as well as associated and unassociated data communications.
TABLE 1DEVICEFREQUENCY RANGEIn-band tuner for Television Programming54 Mhz to 860 MhzOut-of-band tuner for Data70 Mhz to 130 MhzOut-of-band Upstream Transmitter for Data5 Mhz to 42 MhzCable Modem Tuner for Data88 Mhz to 860 MhzCable Modem Upstream Transmitter for Data5 Mhz to 42 Mhz
In designing a television system or set-top box system that accommodates each of the signals in TABLE 1, a major challenge is to minimize insertion loss for signals coming downstream from the cable head end and destined for the tuners while simultaneously minimizing the upstream insertion loss for the upstream data with appropriate isolation of the signals. If the insertion loss from cable to tuner is too great, the sensitivity of the set-top box (or television) may be degraded and cause problems with data error or picture and sound quality. If insertion loss is too great in the upstream path to the cable, higher output power amplifiers may be required with a substantial amount of energy being dissipated as losses before the output signal reaches the cable. This results in wasted energy and increased cost of the set-top box.